In a distributed virtual infrastructure characterized by arrays of virtual storage devices (logical units or LUNs) being accessed by virtual computing devices (virtual machines or VMs), there is an inability to ensure quality-of-service (QoS) delivery from the storage arrays to the VMs.
Traditionally, servers were attached to a storage network and LUNs were allocated to the servers. Examples of such storage networks include, for example, an Internet Small Computer System Interface (iSCSI) network, a Fibre Channel (FC) network, a Fibre Channel over Ethernet (FCoE) network, and an Infiniband network. In these traditional systems, the required network bandwidth and load on storage (in terms of input/output operations per second or IOPS) was fairly consistent and predictable.
However, in a virtualized environment, issues associated with VM over-subscription (i.e., running too many VMs on too few physical processing devices), VM abstraction (i.e., not being able to easily determine which physical processing devices are hosting which VMs), and VM explosion (i.e., a rapid instantiation of a large number of VMs) make it difficult to diagnose performance contention issues.